.rxb{
    text-align: center;
}

.jieshao{
    text-align: center;
}

.up{
    font-size: 50px;
    color: black;
    text-align: center;
}

.up1{
    font-size: 30px;
    color: black;
    text-align: left;
    text-align: center;
}

.col-md-4{
    height: 250px;
    text-align: center;
}

.foot{
    background-color: black;
    text-align: center;
}